Logic circuit module, method for designing a semiconductor integrated circuit using the same, and semiconductor integrated circuit

ABSTRACT

A logic circuit module is used for designing a semiconductor integrated circuit using an FPGA (Field Programmable Gate Array) or a short-term gate array. Provided that a seventh input terminal of the logic circuit module is fixed to the power supply, a third multiplexer always selects the output of a second multiplexer, and a signal selected by the second multiplexer is directly output to a second output terminal. Moreover, an AND circuit always outputs an output signal of a first multiplexer to a first output terminal. Thus, fixing the seventh input terminal to the power supply causes respective logics formed from the first multiplexer and the second multiplexer to be separated by the third multiplexer, allowing for independent representation of the logics. Accordingly, the area efficiency of the logic circuit module is improved, resulting in reduction in size of the semiconductor integrated circuit.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a logic circuit module havingexcellent area efficiency and capable of representing a large number oflogics, a method for designing a semiconductor integrated circuit usingsuch a logic circuit module, and a semiconductor integrated circuit.

[0002] In an FPGA (Field Programmable Gate Array), a device is firstmanufactured in such a form that can be used for general purposes, sothat a desired circuit operation is implemented by writing data tostorage elements incorporated in advance into the device or blowingfuses.

[0003] In general, a gate array is produced in advance up to atransistor portion, so that a desired circuit operation is implementedusing all wiring layers. However, there is also a short-term gate arrayin order to implement a desired circuit in a shorter period. In theshort-term gate array, not all of the wiring layers are produced inadvance. Instead, some of the wiring layers are produced in advance, sothat a desired circuit is formed using only the remaining wiring layers.

[0004] Moreover, in a cell base IC (Integrated Circuit), correctionmacro cells are incorporated in advance in order to quickly handle anyerroneous circuit design found in the manufactured cell base IC. Thus,when the necessity for correction arises, only the wiring layers arecorrected using the correction macro cells.

[0005] Such an FPGA and short-term gate array have a small amount ofindividually modifiable wiring resources for forming a semiconductorintegrated circuit implementing a desired operation. Therefore, not asmall unit like a transistor but a logic module capable of implementinga large number of logics by a single unit is used as a base unit forimplementing a logic, in order to reduce the amount of individuallymodifiable wirings. A method for designing a semiconductor integratedcircuit in such a conventional FPGA and short-term gate array will nowbe described in connection with FIGS. 16A and 16B. Conventionally, asshown in FIG. 16A, a multiplicity of 4-1 multiplexers M13 are used aslogic circuit modules in order to form a logic circuit in such a formthat can be used for general purposes. Each input terminal of the logiccircuit module M13 is connected to a power supply, ground or externalwiring, thereby expressing a plurality of types of logic circuits. FIG.16B shows an example of a NAND logic implemented with the logic circuitmodule M13. In FIG. 16B, input terminals TI1311, TI1312 and TI1313 areconnected to a power supply, an input terminal TI1314 is grounded, andinput terminals TI1315 and TI1316 are respectively connected to externalinput terminals A13 and A14. An output terminal TO1311 is connected toan external output terminal Y13. Thus, a NAND output of the externalinput terminals A13 and A14 is output to the external output terminalY13.

[0006] A conventional implementation method in which macro cells areincorporated in advance for correction on the cell base IC will now bedescribed in connection with FIGS. 13A to 13C. FIG. 13A shows anuncorrected, original circuit. In this circuit, an OR logic circuit C314obtains an OR logic of respective outputs of logic circuits C311, C312and C313, and applies the OR logic output to an input of a logic circuitC315. It is now assumed that this circuit should be corrected so as toapply an AND logic of the logic circuits C311, C312 and C313 to theinput of the logic circuit C315 instead of the OR logic. FIG. 13C showsan example of the circuit corrected using NAND macro cells incorporatedin advance. The dashed lines in the figure indicate a corrected portion.In this example, four NAND macro cells are used for correction.

[0007] In the conventional FPGA and short-term gate array, the logiccircuit module M13 of FIGS. 16A and 16B is capable of representing allof two-input logic circuits, but has a larger area than that of anindividually implemented two-input logic circuit. In particular, asingle logic circuit module is required even if only a basic gate isnecessary. This results in extremely disadvantageous area efficiency inthe case of a semiconductor integrated circuit that merely requires alarge number of basic gates. Thus, the resultant semiconductorintegrated circuit has a large size. A semiconductor integrated circuitfor digital signal processing uses a large number of adders as itscircuit portion. In designing such a semiconductor integrated circuit,the adders cannot be efficiently implemented in terms of the area.Moreover, in the case of a semiconductor integrated circuit using alarge number of at least three-input logic circuits, a desiredsemiconductor integrated circuit can be reduced in size with improvedarea efficiency if the at least three-input logic circuits can beimplemented with a logic circuit module. In fact, however, the logiccircuit module M13 can implement only a small number of types of atleast three-input logic circuits. Therefore, the resultant semiconductorintegrated circuit has an extremely large size.

[0008] Moreover, in the correction of a cell base IC, a portion to becorrected of a designed semiconductor circuit cannot be predicted, andNAND macro cells to be incorporated in advance must be distributed allover the semiconductor circuit. Accordingly, a long wiring length islikely to be required for partial correction, and the number of wiringlayers to be modified for correction is likely to be increased. Macrocells to be incorporated in advance normally use basic gates, andtherefore a large number of wiring layers are required for correction.As a result, even a slight increase in circuit scale to be correctedmakes the correction difficult.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to improve the structureof a logic circuit module so as to increase the area efficiency of thelogic circuit module when implementing various logic gates in an FPGAand a short-term gate array, and thus reduce the size of the resultantsemiconductor integrated circuit. It is another object of the presentinvention to reduce the wiring length for correction by using improvedlogic circuit modules as macro cells to be incorporated in advance inpreparation for correction of a cell base IC. It is still another objectof the present invention to reduce the number of wiring layers to bemodified for correction so as to enable correction to be made in anexcellent manner even if the circuit scale to be corrected is somewhatincreased.

[0010] In order to achieve these objects, the present invention enablesa plurality of logic functions to be represented with a single logiccircuit module, and also enables a half adder to be formed with a singlelogic circuit module.

[0011] More specifically, a logic circuit module according to thepresent invention is characterized in that it comprises a plurality ofinput terminals, a plurality of output terminals, and a plurality oflogic elements provided between the plurality of input terminals and theplurality of output terminals, the plurality of input terminals are eachconnected to an external signal line, a power supply or a ground so asto implement a plurality of desired logic functions, and at least two ofthe implemented plurality of logic functions are such that a potentialstate of an output terminal corresponding to one of the logic functionsis not affected by a potential state of an input terminal correspondingto the other logic function.

[0012] The logic circuit module according to the present invention ischaracterized in that at least one of the plurality of logic elementsseparates at least two of the implemented plurality of logic functionsfrom each other so as to make the two logic functions independent ofeach other.

[0013] A logic circuit module according to the present invention ischaracterized in that it comprises first to seventh input terminals,first and second output terminals, and first to third 2-1 multiplexers,the first 2-1 multiplexer has its two signal terminals respectivelyconnected to the first and second input terminals, and its selectionterminal connected to the third input terminal, the second 2-1multiplexer has its two signal terminals respectively connected to thefourth and fifth input terminals, and its selection terminal connectedto the sixth input terminal, the third 2-1 multiplexer has its twosignal terminals respectively connected to signals selected by the firstand second 2-1 multiplexers, and its selection terminal connected to theseventh input terminal, the first output terminal receives the signalselected by the first 2-1 multiplexer, and the second output terminalreceives a signal selected by the third 2-1 multiplexer.

[0014] The logic circuit module according to the present invention ischaracterized in that it further comprises a two-input AND circuit, theAND circuit receives the signal selected by the first 2-1 multiplexer,the seventh input terminal is connected to the AND circuit, and thefirst output terminal receives an output signal of the AND circuit.

[0015] The logic circuit module according to the present invention ischaracterized in that the third input terminal serves also as the sixthinput terminal.

[0016] The logic circuit module according to the present invention ischaracterized in that the first, third, fourth and sixth input terminalsare respectively connected to external signal lines, and the second,fifth and seventh input terminals are connected to a power supply,thereby implementing two independent OR logics.

[0017] The logic circuit module according to the present invention ischaracterized in that the first and fourth input terminals are connectedto a ground, the seventh input terminal is connected to a power supply,and the second, third, fifth and sixth input terminals are respectivelyconnected to external signal lines, thereby implementing two independentAND logics.

[0018] The logic circuit module according to the present invention ischaracterized in that the first to sixth input terminals arerespectively connected to external signal lines, and the seventh inputterminal is connected to a power supply, thereby implementing twoindependent 2-1 multiplexer logics.

[0019] The logic circuit module according to the present invention ischaracterized in that the first and fifth input terminals are connectedto a ground, the second and fourth input terminals are connected to apower supply, the third and sixth input terminals are connected to acommon external signal line, and the seventh input terminal is connectedto another external signal line so as to form an EX-OR logic and an ANDlogic each receiving as inputs two signals of the common external signalline and the another external signal line, thereby implementing a halfadder.

[0020] A semiconductor integrated circuit according to the presentinvention is characterized in that it comprises four logic circuitmodules each implementing the half adder, and a single logic circuitmodule implementing the two OR logics, and a lower-bit full adder isformed from two of the four logic circuit modules each implementing thehalf adder and one of the two OR logics implemented by the logic circuitmodule, and an upper-bit full adder is formed from the other two logiccircuit modules each implementing the half adder and the other OR logicimplemented by the logic circuit module, thereby implementing a 2-bitfull adder.

[0021] The logic circuit module according to the present invention ischaracterized in that the second, fifth and sixth input terminals arerespectively connected to external signal lines, the first inputterminal is connected to a ground, the seventh input terminal isconnected to a power supply, the third input terminal is connected tothe second output terminal, and the fourth input terminal is connectedto the first output terminal so as to form an AND logic and a 2-1multiplexer that are independent of each other, and an output of the ANDlogic is connected to one of two signal terminals of the 2-1multiplexer, thereby implementing a storage circuit having a resetfunction.

[0022] The logic circuit module according to the present invention ischaracterized in that the second and seventh input terminals areconnected to a power supply, the first, fifth and sixth input terminalsare respectively connected to external signal lines, the third inputterminal is connected to the second output terminal, and the fourthinput terminal is connected to the first output terminal so as to forman OR logic and a 2-1 multiplexer that are independent of each other,and an output of the OR logic is connected to a signal terminal of the2-1 multiplexer, thereby implementing a storage circuit having a setfunction.

[0023] Moreover, a method for designing a semiconductor integratedcircuit according to the present invention is characterized in that thesemiconductor integrated circuit includes a plurality of logic circuitmodules, and the semiconductor integrated circuit conducting aprescribed operation is designed by connecting the input terminals ofthe logic circuit modules to a power supply or ground, or connecting aninput terminal of a logic circuit module to an output terminal ofanother logic circuit module.

[0024] The method according to the present invention is characterized bydesigning the semiconductor integrated circuit conducting the prescribedoperation by forming in advance longitudinal and lateral wirings forconnecting the input terminals of the logic circuit modules to the powersupply or ground, or connecting the input terminals of the logic circuitmodules to the output terminals thereof, and a plurality of connectingmeans for connecting the longitudinal and lateral wirings to each other,and then programming so as to connect prescribed longitudinal andlateral wirings to each other through a prescribed one of the pluralityof connecting means.

[0025] A method for designing a semiconductor integrated circuitaccording to the present invention is characterized by manufacturing thesemiconductor integrated circuit with the logic circuit moduleincorporated therein, and when necessity for correction of themanufactured semiconductor integrated circuit arises, correcting thesemiconductor integrated circuit by connecting a wiring to theincorporated logic circuit module.

[0026] Thus, the present invention is capable of implementing at leasttwo independent logic circuits per logic circuit module. Therefore, thearea efficiency of the logic circuit module is improved over theconventional example in which only a single logic circuit is implementedper logic circuit module. Moreover, the required number of logic circuitmodules is reduced, allowing for reduction in area of a wiring regionprovided for wirings that connect the logic circuit modules to eachother. As a result, a designed semiconductor integrated circuit isreduced in size. Moreover, each logic circuit module of the presentinvention has a plurality of output terminals. Therefore, the logiccircuit module of the present invention can represent an increasednumber of types of logic circuits as compared to the conventional logiccircuit module having only one output terminal. For example, the logiccircuit module of the present invention can represent a half adder,which cannot be represented with a single logic circuit module in theconventional example.

[0027] Moreover, according to the present invention, the logic circuitmodule of the present invention is incorporated in advance into thesemiconductor integrated circuit for the purpose of correcting a cellbase IC. Therefore, even when the necessity for correction of themanufactured semiconductor integrated circuit arises, two or more logiccircuits can be integrated into a single logic circuit module, wherebythe wiring length for connecting the required logic circuits to eachother as well as the number of wiring layers to be modified forcorrection are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a diagram showing an example of a logic circuit moduleaccording to an embodiment of the present invention;

[0029]FIG. 2A is a diagram showing an exemplary structure of a CMOS(Complementary Metal-Oxide Semiconductor) circuit for implementing thelogic circuit module, and FIG. 2B is a diagram showing an equivalentcircuit of the CMOS circuit;

[0030]FIGS. 3A and 3B are diagrams showing the connection forimplementing two independent OR logics using the logic circuit module;

[0031]FIGS. 4A and 4B are diagrams showing the connection forimplementing two independent AND logics using the logic circuit module;

[0032]FIGS. 5A and 5B are diagrams showing the connection forimplementing two independent 2-1 multiplexer logics using the logiccircuit module;

[0033]FIGS. 6A and 6B are diagrams showing the connection forimplementing a half adder using the logic circuit module;

[0034]FIG. 7 is a diagram showing the connection for implementing a2-bit full adder using the logic circuit module;

[0035]FIGS. 8A and 8B are diagrams showing the connection forimplementing a resettable storage circuit using the logic circuitmodule;

[0036]FIGS. 9A and 9B are diagrams showing the connection forimplementing a settable storage circuit using the logic circuit module;

[0037]FIG. 10 is a conceptual diagram showing an example of an FPGAsemiconductor device formed using the logic circuit module of theembodiment;

[0038]FIG. 11 is a conceptual diagram showing an example of a 2-bit fulladder implemented using the FPGA semiconductor device;

[0039]FIG. 12A is a diagram showing an example of verilog-HDL (HardwareDescription Language) description of a 2-1 multiplexer, and FIG. 12B isa diagram showing an example of an equivalent circuit of thedescription;

[0040]FIG. 13A is a diagram showing an uncorrected circuit manufacturedwith the logic circuit module incorporated into a cell base IC, FIG. 13Bis a diagram illustrating a manner of correcting the uncorrected circuitusing the logic circuit module, and FIG. 13C is a diagram illustrating amanner of correcting the circuit using NAND macro cells incorporated inadvance into the cell base IC according to a conventional example;

[0041]FIG. 14 is a diagram showing a first modification of the logiccircuit module;

[0042]FIG. 15 is a diagram showing a second modification of the logiccircuit module; and

[0043]FIG. 16A is a diagram showing an example of a logic circuit modulefor use in a conventional FPGA and gate for short-term development, andFIG. 16B is a diagram showing an example of the connection implementinga NAND circuit using the logic circuit module.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Hereinafter, embodiments of a logic circuit module, a method fordesigning a semiconductor integrated circuit using the same, and asemiconductor integrated circuit according to the present invention willbe described in detail with reference to the accompanying drawings.

Logic Circuit Module

[0045] An exemplary logic circuit module according to an embodiment ofthe present invention is shown in FIG. 1. In FIG. 1, a logic circuitmodule M1 has first to seventh input terminals TI111, TI112, TI113,TI121, TI122, TI123, TI131, first and second output terminals TO11,TO12, first to third 2-1 multiplexers (logic elements) C11, C12, C13,and a single 2-input AND circuit (logic element) C14.

[0046] The first and second input terminals TI111 and TI112 arerespectively connected to two signal terminals of the first multiplexerC11, and the third input terminal TI113 is connected to a selectionterminal of the first multiplexer C11. The first multiplexer C11 selectsa signal of the second input terminal TI112 when a potential at thethird input terminal TI113 is at H (High) level, and selects a signal ofthe first input terminal TI111 when the potential at the third inputterminal TI113 is at L (Low) level. Similarly, the fourth and fifthinput terminals TI121 and TI122 are respectively connected to two signalterminals of the second multiplexer C12, and the sixth input terminalTI123 is connected to a selection terminal of the second multiplexerC12. The second multiplexer C12 selects a signal of the fifth inputterminal TI122 when a potential at the sixth input terminal TI123 is atH level, and selects a signal at the fourth input terminal TI121 when apotential at the sixth input terminal TI123 is at L level.

[0047] The signals selected by the first and second multiplexers C11 andC12 are respectively connected to two signal terminals of the thirdmultiplexer C13, and the seventh input terminal TI131 is connected to aselection terminal of the third multiplexer C13. The third multiplexerC13 selects an output signal of the second multiplexer C12 when apotential at the seventh input terminal TI131 is at H level, and selectsan output signal of the first multiplexer C11 when a potential at theseventh input terminal TI131 is at L level. The signal selected by thethird multiplexer C13 is output to the second output terminal TO12.

[0048] The signal selected by the first multiplexer C11 is output to oneinput terminal of the two-input AND circuit C14, and the seventh inputterminal TI131 is connected to the other input terminal thereof. Anoutput of the AND circuit C14 is directly output to the first outputterminal TO11.

[0049] Provided that the seventh input terminal TI131 of the logiccircuit module M1 is fixed to the power supply, the third multiplexerC13 always selects the output of the second multiplexer C12, and thesignal selected by the second multiplexer C12 is directly output to thesecond output terminal TO12. Moreover, the AND circuit C14 alwaysoutputs the output signal of the first multiplexer C11 to the firstoutput terminal TO11. Thus, fixing the seventh input terminal TI131 tothe power supply causes the respective logics formed from the firstmultiplexer C11 and the second multiplexer C12 to be separated by thethird multiplexer C13, allowing for independent representation of thelogics.

[0050] Hereinafter, an example of the logic circuit module M1implemented in a CMOS circuit device will be described in connectionwith FIGS. 2A and 2B.

[0051] In FIGS. 2A and 2B, the same reference numerals and characters asthose of FIG. 1 denote the same components. Connecting P-channel andN-channel CMOS transistors to each other as shown in FIG. 2A results inan equivalent circuit of FIG. 2B. A logic circuit module M6 is logicallyequivalent to the logic circuit module M1 of FIG. 1.

Two Independent OR Circuits

[0052] In FIGS. 3A and 3B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 3A, thesecond, fifth and seventh input terminals TI112, TI122 and TI131 of thelogic circuit module M1 are connected to the power supply. As shown inFIG. 3B, such a structure enables the following two OR logics to beimplemented independently of each other: an OR logic having the firstand third input terminals TI111 and TI113 as its inputs and the firstoutput terminal TO11 as its output; and an OR logic having the fourthand sixth input terminals TI121 and TI123 as its inputs and the secondoutput terminal TO12 as its output. In other words, a potential state ofthe output terminal TO11 of one OR logic is not affected by respectivepotential states of the input terminals TI121 and TI123 of the other ORlogic, and a potential state of the output terminal TO12 of the other ORlogic is not affected by respective potential states of the inputterminals TI111 and TI113 of one OR logic. Other implementation examplesof such two independent logics are shown in FIGS. 4A, 4B and 5A, 5B.

Two Independent AND Circuits

[0053] In FIGS. 4A and 4B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 4A, thefirst and fourth input terminals TI111 and TI121 of the logic circuitmodule M1 are grounded, and the seventh input terminal TI131 thereof isconnected to the power supply. As shown in FIG. 2B, such a structureenables the following two AND logics to be implemented independently ofeach other: an AND logic having the second and third input terminalsTI112 and TI113 as its inputs and the first output terminal TO11 as itsoutput; and an AND logic having the fifth and sixth input terminalsTI122 and TI123 as its inputs and the second output terminal TO12 as itsoutput.

Two Independent 2-1 Mmultiplexer Logics

[0054] In FIGS. 5A and 5B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 5A, theseventh input terminal TI131 of the logic circuit module M1 is connectedto the power supply. As shown in FIG. 5B, such a structure enables thefollowing two 2-1 multiplexer logics to be implemented independently ofeach other: a 2-1 multiplexer logic having the first and second inputterminals TI111 and TI112 as its signal inputs, the third input terminalTI113. as its selection signal, and the first output terminal TO11 asits output; and a 2-1 multiplexer logic having the fourth and fifthinput terminals TI121 and TI122 as its signal inputs, the sixth inputterminal TI123 as its selection signal, and the second output terminalTO12 as its output.

[0055] Hereinafter, description will be given in connection with FIGS.6A and 6B that the logic circuit module M1 of FIG. 1 can be used as ahalf adder.

Half Adder

[0056] In FIGS. 6A and 6B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 6A, in thelogic circuit module M1, the first and fifth input terminals TI111 andTI122 are grounded, the second and fourth input terminals TI112 andTI121 are connected to the power supply, and the third and sixth inputterminals TI113 and TI123 are connected together into an external inputterminal TI611. As shown in FIG. 6B, such a structure enables a halfadder to be implemented. This half adder has the seventh input terminalTI131 as its addition input, the second output terminal TO12 as itsaddition result output, and the first output terminal TO11 as its carryoutput.

2-bit Full Adder

[0057] Hereinafter, an example of a 2-bit full adder will now bedescribed in connection with FIG. 7. This 2-bit full adder uses fourcircuits each having a function of the half adder shown in FIGS. 6A and6B, and a single circuit having two independent OR functions shown inFIGS. 3A and 3B.

[0058] In FIG. 7, the same reference numerals and characters as those ofFIGS. 1, 3A, 3B, 6A and 6B denote the same components. In FIG. 7, FA2denotes a 2-bit full adder. The 2-bit full adder FA2 adds 2-bit additiondata 1 (A1, A2 from the lower bit), 2-bit addition data 2 (B1, B2 fromthe lower bit) and a carry CY_IN from the lower order to the 2-bitadder, and outputs the addition result (two bits) to output terminals S1and S2 from the lower bit, as well as outputs the carry to an outputterminal CY_OUT.

[0059] In FIG. 7, HA denotes a logic circuit module performing afunction of the half adder as shown in FIGS. 6A and 6B, and OR2 denotesa logic circuit module performing two independent OR functions as shownin FIGS. 3A and 3B. The circuits in the half adders HA and theindependent two OR functions OR2 are equivalent circuits that are shownin a simplified manner for convenience in order to facilitateunderstanding of the operation. The use of four logic circuit moduleseach operating as half adder HA and a single logic circuit moduleoperating as two independent ORs as shown in FIG. 7 enablesconfiguration of a 2-bit full adder.

Resettable Storage Circuit

[0060] Hereinafter, an example of a resettable storage circuitconfigured using the logic circuit module of FIG. 1 will be described inconnection with FIGS. 8A and 8B.

[0061] In FIGS. 8A and 8B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 8A, in thelogic circuit module M1, the first input terminal TI111 is grounded, theseventh input terminal TI131 is connected to the power supply, thefourth input terminal TI121 and the first output terminal TO11 areconnected to each other, and the third input terminal TI113 and thesecond output terminal TO12 are connected to each other. As shown inFIG. 8B, such a structure enables a resettable storage circuit to beconfigured. This resettable storage circuit has the second inputterminal TI112 as its reset input, the fifth input terminal TI122 as itsdata input, the sixth input terminal TI123 as its data fetch/holdselection input, and an external output terminal Q connected to thefirst output terminal TO11 as its data output.

Settable Storage Circuit

[0062] Hereinafter, an example of a settable storage circuit configuredusing the logic circuit module of FIG. 1 will be described withreference to FIGS. 9A and 9B.

[0063] In FIGS. 9A and 9B, the same reference numerals and characters asthose of FIG. 1 denote the same components. As shown in FIG. 9A, in thelogic circuit module M1, the second and seventh input terminals TI112and TI131 are connected to the power supply, the fourth input terminalTI121 and the first output terminal TO11 are connected to each other,and the third input terminal TI113 and the second output terminal TO12are connected to each other. As shown in FIG. 9B, such a structureenables a settable storage circuit to be configured. This settablestorage circuit has the first input terminal TI111 as its set input, thefifth input terminal TI122 as its data input, the sixth input terminalTI123 as its data fetch/hold selection input, and an external outputterminal Q connected to the first output terminal TO11 as its dataoutput.

FPGA Using the Logic Circuit Module

[0064] Hereinafter, an example of a FPGA semiconductor device using thelogic circuit module M1 of FIG. 1 in the FPGA will be described inconnection with FIGS. 10 and 11.

[0065]FIG. 10 shows the concept of the FPGA using the logic circuitmodule M1 of FIG. 1. In FIG. 10, M1 denotes a logic circuit moduleimplementing the logic shown in FIG. 1, and I4 denotes input terminalsof the logic circuit module M1, which correspond to the input terminalsTI111, TI112, TI113, TI121, TI122, TI123 and TI131 of FIG. 1 from theleft. Moreover, O4 denotes output terminals of the logic circuit moduleM1, which corresponds to the output terminals TO11 and TO12 from thetop. The longitudinal and lateral solid lines in FIG. 10 representwirings w within the FPGA, which are formed in adjacent wiring layers.Circles at the intersections of the longitudinal and lateral wirings wrepresent so-called anti-fuses (connecting means) h. These anti-fuses hare located in a wiring layer between the longitudinal and lateralwirings w located adjacent to each other. Prior to programming, thelongitudinal and lateral wirings w are insulated from each other.

[0066] An example of the programmed FPGA of FIG. 10 is shown in FIG. 11.FIG. 11 shows an example of the 2-bit full adder of FIG. 7 implementedwith the FPGA of FIG. 10. In FIG. 11, the same reference numerals andcharacters as those of FIGS. 7 and 10 denote the same components. InFIG. 11, black circles at the intersections of the longitudinal andlateral wirings w indicate that a corresponding insulated anti-fuse isblown so as to connect the corresponding longitudinal and lateralwirings w to each other.

[0067] This example is described with respect to the anti-fuses.However, instead of using the anti-fuses, the source and drain portionsof pass transistors may be respectively connected to the longitudinaland lateral wirings w, as well as the outputs of storage elements suchas SRAMs (Static Random Access Memories) may be respectively connectedto the gates of the pass transistors. This results in an SRAM-type FPGAthat is programmable by rewriting the storage elements. Alternatively,the anti-fuses may be replaced with vias for connecting the longitudinaland lateral wirings w. In this case, a gate array can be implementedwhich is capable of changing the circuit operation of the semiconductordevice by merely replacing masks of the vias during manufacturing.

[0068] As has been described above, with the logic circuit module M1 ofthe present embodiment shown in FIG. 1, two independent logic circuitscan be implemented per logic circuit module, allowing for improved areaefficiency even in a semiconductor integrated circuit using a largenumber of two-input logic circuits. For example, in the case ofimplementing two 2-1 multiplexers, the CMOS logic circuit module of thepresent invention exemplified in FIGS. 2A and 2B is formed from 32transistors. In contrast, the logic circuit module of the conventionalexample shown in FIG. 16 is formed from 26 transistors when implementedwith the same structure as that of FIGS. 2A and 2B. Since two logiccircuit modules are necessary, a total of 52 transistors are required.Accordingly, the logic circuit module M1 of the present embodiment shownin FIG. 1 allows for significant improvement in area efficiency over theconventional logic circuit module of FIG. 16. Moreover, the use of theconventional logic circuit module requires a region for wirings thatconnect the two logic circuit modules to each other. However, the logiccircuit module M1 of the present embodiment does not require such awiring region, resulting in a compact semiconductor integrated circuit.The 2-1 multiplexer logic is described in the verilog-HDL as shown inFIG. 12A, and an exemplary equivalent circuit thereof is commonly usedas the circuit shown in FIG. 12B. Therefore, the logic circuit module M1of the present embodiment shown in FIG. 1 is practically effective.

Method For Designing A Semiconductor Integrated Circuit Using the LogicCircuit Module

[0069] Hereinafter, an example of a semiconductor integrated circuitwill be described in connection with FIGS. 13A to 13C. In this example,a cell base IC having the logic circuit module M1 of FIG. 1 incorporatedtherein is manufactured, and correction is made with the logic circuitmodule when the necessity for circuit correction arises.

[0070] In FIGS. 13A to 13C, the same reference numerals and charactersas those of FIG. 1 denote the same components. FIG. 13A shows anuncorrected, original circuit. In this circuit, the OR logic circuitC314 obtains an OR logic of respective outputs of the logic circuitsC311, C312 and C313, and applies the OR logic output to the input ofanother logic circuit C315. It is now assumed that this circuit shouldbe corrected so as to apply an AND logic of the logic circuits C311,C312 and C313 to the input of the logic circuit C315 instead of the ORlogic. FIG. 13B shows an example of the circuit corrected using thelogic circuit module M1 of FIG. 1 incorporated in advance. In FIG. 13B,the dashed lines indicate a corrected portion. In FIG. 13B, M1 denotes alogic circuit module that has been incorporated in advance, and acircuit within the module M1 is an equivalent circuit shown in asimplified manner for convenience. As shown in connection with FIGS. 4Aand 4B, the logic circuit module M1 has its seventh input terminal TI131connected to the power supply and its first and fourth input terminalsTI111 and TI121 grounded, thereby internally implementing twoindependent AND logics. Connecting the output of one of the twoindependent AND logics (the first output terminal TO11 in the figure) toone input of the other AND logic (the input terminal TI123 in theexample of the figure) through a wiring CON5 results in a three-inputAND logic circuit having the three input terminals TI112, TI113 andTI122 as its inputs and the output terminal TO12 as its output, as shownin the logic circuit module M1 for convenience. The correction can bemade as follows: the inputs of the three-input AND logic circuit arerespectively connected to wirings CON1, CON2 and CON3 connecting to therespective inputs of the logic circuit C314, and a wiring connecting tothe output of the logic circuit C314 is disconnected (shown by CUT1 inthe figure) so that the output of the three-input AND logic circuit isconnected to the input of the logic circuit C315 through a wiring CON4.

First Modification of the Logic Circuit Module

[0071]FIG. 14 shows a first modification of the logic circuit module.The structure of the logic circuit module M2 of FIG. 14 is generally thesame as that of the logic circuit module M1 of FIG. 1 except that thetwo-input AND circuit C14 is eliminated so that the signal selected bythe 2-1 multiplexer C11 is directly output to the output terminal TO11.The logic circuit module M2 of this modification enables implementationof the two independent logic circuits of FIGS. 3B, 4B, 5B, 8B and 9B.

Second Modification of Logic Circuit Module

[0072]FIG. 15 shows a second modification of the logic circuit module.In the logic circuit module M3 of FIG. 15, the third input terminalTI113 of the logic circuit module M2 of FIG. 14 serves also as the sixthinput terminal TI123. The logic circuit module M2 of this modificationenables implementation of the two independent logic circuits of FIGS.3B, 4B and 5B.

[0073] Although the two modifications of the logic circuit module havebeen described, the present invention is not limited to them. Forexample, the logic elements included in the logic circuit module of thepresent invention are not limited to the three 2-1 multiplexers. Thelogic circuit module of the present invention may include four or moremultiplexers. Alternatively, the logic circuit module of the presentinvention may include logic elements other than the 2-1 multiplexers.Moreover, the logic circuit module of the present invention may includeany number of output terminals instead of the two output terminals.

What is claimed is:
 1. A logic circuit module, characterized in that itcomprises a plurality of input terminals, a plurality of outputterminals, and a plurality of logic elements provided between theplurality of input terminals and the plurality of output terminals, theplurality of input terminals are each connected to an external signalline, a power supply or a ground so as to implement a plurality ofdesired logic functions, and at least two of the implemented pluralityof logic functions are such that a potential state of an output terminalcorresponding to one of the logic functions is not affected by apotential state of an input terminal corresponding to the other logicfunction.
 2. The logic circuit module according to claim 1,characterized in that at least one of the plurality of logic elementsseparates at least two of the implemented plurality of logic functionsfrom each other so as to make the two logic functions independent ofeach other.
 3. A logic circuit module, characterized in that itcomprises first to seventh input terminals, first and second outputterminals, and first to third 2-1 multiplexers, the first 2-1multiplexer has its two signal terminals respectively connected to thefirst and second input terminals, and its selection terminal connectedto the third input terminal, the second 2-1 multiplexer has its twosignal terminals respectively connected to the fourth and fifth inputterminals, and its selection terminal connected to the sixth inputterminal, the third 2-1 multiplexer has its two signal terminalsrespectively connected to signals selected by the first and second 2-1multiplexers, and its selection terminal connected to the seventh inputterminal, and the first output terminal receives a signal selected bythe first 2-1 multiplexer, and the second output terminal receives asignal selected by the third 2-1 multiplexer.
 4. The logic circuitmodule according to claim 3, characterized in that it further comprisesa two-input AND circuit, the AND circuit receives the signal selected bythe first 2-1 multiplexer, and the seventh input terminal is connectedto the AND circuit, and the first output terminal receives an outputsignal of the AND circuit.
 5. The logic circuit module according toclaim 1 or 2, characterized in that the third input terminal serves alsoas the sixth input terminal.
 6. The logic circuit module according toclaim 3, characterized in that the first, third, fourth and sixth inputterminals are respectively connected to external signal lines, and thesecond, fifth and seventh input terminals are connected to a powersupply, thereby implementing two independent OR logics.
 7. The logiccircuit module according to claim 3 or 4, characterized in that thefirst and fourth input terminals are connected to a ground, the seventhinput terminal is connected to a power supply, and the second, third,fifth and sixth input terminals are respectively connected to externalsignal lines, thereby implementing two independent AND logics.
 8. Thelogic circuit module according to claim 3 or 4, characterized in thatthe first to sixth input terminals are respectively connected toexternal signal lines, and the seventh input terminal is connected to apower supply, thereby implementing two independent 2-1 multiplexerlogics.
 9. The logic circuit module according to claim 4, characterizedin that the first and fifth input terminals are connected to a ground,the second and fourth input terminals are connected to a power supply,the third and sixth input terminals are connected to a common externalsignal line, and the seventh input terminal is connected to anotherexternal signal line so as to form an EX-OR logic and an AND logic eachreceiving as inputs two signals of the common external signal line andthe another external signal line, thereby implementing a half adder. 10.A semiconductor integrated circuit, characterized in that it comprisesfour logic circuit modules each implementing the half adder of claim 9,and a single logic circuit module implementing the two OR logics ofclaim 6, and a lower-bit full adder is formed from two of the four logiccircuit modules each implementing the half adder and one of the two ORlogics implemented by the logic circuit module, and an upper-bit fulladder is formed from the other two logic circuit modules eachimplementing the half adder and the other OR logic implemented by thelogic circuit module, thereby implementing a 2-bit full adder.
 11. Thelogic circuit module according to claim 3 or 4, characterized in thatthe second, fifth and sixth input terminals are respectively connectedto external signal lines, the first input terminal is connected to aground, the seventh input terminal is connected to a power supply, thethird input terminal is connected to the second output terminal, and thefourth input terminal is connected to the first output terminal so as toform an AND logic and a 2-1 multiplexer that are independent of eachother, and an output of the AND logic is connected to one of two signalterminals of the 2-1 multiplexer, thereby implementing a storage circuithaving a reset function.
 12. The logic circuit module according to claim3 or 4, characterized in that the second and seventh input terminals areconnected to a power supply, the first, fifth and sixth input terminalsare respectively connected to external signal lines, the third inputterminal is connected to the second output terminal, and the fourthinput terminal is connected to the first output terminal so as to forman OR logic and a 2-1 multiplexer that are independent of each other,and an output of the OR logic is connected to a signal terminal of the2-1 multiplexer, thereby implementing a storage circuit having a setfunction.
 13. A method for designing a semiconductor integrated circuit,characterized in that the semiconductor integrated circuit includes aplurality of logic circuit modules of claim 1, 2, 3 or 4, and thesemiconductor integrated circuit conducting a prescribed operation isdesigned by connecting the input terminals of the logic circuit modulesto a power supply or ground, or connecting an input terminal of a logiccircuit module to an output terminal of another logic circuit module.14. The method according to claim 13, characterized by designing thesemiconductor integrated circuit conducting the prescribed operation byforming in advance longitudinal and lateral wirings for connecting theinput terminals of the logic circuit modules to the power supply orground, or connecting the input terminals of the logic circuit modulesto the output terminals thereof, and a plurality of connecting means forconnecting the longitudinal and lateral wirings to each other, and thenprogramming so as to connect prescribed longitudinal and lateral wiringsto each other through a prescribed one of the plurality of connectingmeans.
 15. A method for designing a semiconductor integrated circuit,characterized by manufacturing the semiconductor integrated circuit withthe logic circuit module of claim 1, 2, 3 or 4 incorporated therein, andwhen necessity for correction of the manufactured semiconductorintegrated circuit arises, correcting the semiconductor integratedcircuit by connecting a wiring to the incorporated logic circuit module.